The invention is concerned with the mounting of a horn antenna of a Doppler radar apparatus, and more particularly with a novel vibration isolation enclosure which isolates the horn antenna both from externally generated physical vibrations, as well as preferably providing electromagnetic interference/radio frequency interference (EMI/RFI) shielding for a radar transceiver unit and/or other electrical or electronic circuit elements associated with the horn antenna.
While the vibration isolation enclosure in accordance with the invention may find utility in a variety of applications, the description will be facilitated by reference to the specific problem of providing a vibration isolation enclosure for a horn antenna used in a Doppler radar for measuring the rate of travel of a vehicle. More particularly, velocity measuring apparatus for both over-the-road and off-road vehicles are utilized to measure and indicate the cumulative distance traveled as well as the rate of travel or velocity. Especially in off-road vehicles such as farm tractors, construction equipment, or the like, the terrains traveled are rough and uneven, and often the driving wheels of the vehicle experience considerable slippage relative to the ground.
Accordingly, conventional mechanical rotating speedometers, odometers or the like coupled to gearing or other mechanisms associated with the wheels do not necessarily provide accurate measurements of the actual velocity of, or of the distance traveled by, the vehicle relative to the surface over which it is traveling. Such measurements may be used not only for display but also for controlling other apparatus such as material spreader or spray apparatus pulled by or mounted to the vehicle. Such apparatus often require a velocity signal for accurate control of the rate of material or spray distribution thereby.
It has been proposed to utilize Doppler radar apparatus in connection with such off-road vehicles in an effort to avoid the problems associated with uneven terrain and wheel slippage. One such radar apparatus is disclosed for example in U.S. Pat. No. 3,895,384, which is commonly assigned with this application. The foregoing patent discloses directing the Doppler or radar horn antenna at a preferred angle of about 45 degrees relative to the ground, in order to provide optimum results. However, due to the uneven nature of the terrain traveled by such off-road vehicles, it will be appreciated that the Doppler signal provided by the Doppler radar unit will include some component or portion representing multidirectional vibration of the radar unit mounted to the vehicle. It will be appreciated that only the velocity or speed of the vehicle along the ground surface is desired. This is important for accurately determining the net or cumulative distance traveled from time to time by the vehicle over the ground surface. Accordingly, it is desirable to eliminate such other components from the final measurement or determination, if possible.
The foregoing vibration problem causes variations in the Doppler signal corresponding to the vibrations of the radar horn antenna mounted on the vehicle as the vehicle travels along the rough, uneven ground surface. It will be appreciated that with relatively large off-road vehicles on relative rough terrain, multidirectional vibrations can be considerable and these vibrations may readily be transmitted to the horn antenna mounted to a vehicle frame or the like. It will be appreciated that vibration-induced movements of the horn antenna will cause some additional, corresponding small change in the Doppler frequency or signal produced thereby. This vibration-induced component of the Doppler signal will be unrelated to the actual linear or horizontal velocity of the vehicle, and hence comprises an undesirable signal component.
Various improved signal processing systems have been proposed to improve the quality of the Doppler signal produced under such conditions, prior to utilization thereof for display or control of other equipment. One such signal processing system is shown in U.S. Pat. No. Re. 31,851, also assigned to the assignee of record herein.
Additional undesirable signal components may be induced in the related transceiver or other electronic circuits by electromagnetic interference or radio frequency interference (EMI or RFI). Such EMI/RFI induced signal components also bear no relation to the desired linear or horizontal velocity of the vehicle, and hence should be eliminated insofar as possible. In the case of relatively large off-road or farm vehicles, a number of large, rotating metallic parts of the vehicle, or of related machinery being pulled by or mounted to the vehicle may emit considerable electromagnetic interference signals. Accordingly, it is desirable to prevent such extraneous EMI/RFI signals from reaching the transceiver or other electronic circuits associated with the radar unit where they may induce or appear as extraneous noise signals.
While the Doppler radar and signal processing apparatus in accordance with the above-referenced U.S. patents have found widespread commercial success, there is room for yet further improvement. In this regard, the present invention proposes a vibration isolation enclosure for mounting a horn antenna to the vehicle while substantially isolating the horn antenna from vibrations produced or experienced by the vehicle. In this way, the Doppler signal produced by the horn antenna and associated transceiver can be kept substantially free of signal components due to such vibration. Accordingly, the velocity of the vehicle, which it is desired to monitor can be more accurately measured. In accordance with another aspect of the invention, the vibration isolation enclosure also includes an EMI/RFI shielded enclosure portion for mounting or enclosing the transceiver and other electrical or electronic circuits associated with the horn antenna.